A structure (which will be called a nano-structure hereinafter) having tiny holes called nanoholes on its surface is indispensable in the fabrication of magnetic devices, optical devices and quantum-effect devices.
As known methods for fabricating nano-structures, may be mentioned, in addition to photolithography, electron-beam lithography, X-ray beam lithography, etc., that is, fine patterning techniques utilized in semiconductor processing technologies. There are some additional techniques. For example, Furneaux et al. describe a process for producing a nano-structure provided with anode-acidified alumina nanoholes (R. C. Furneaux, W. R. Rigby & A. P. Davidson, “Nature,” 337:147 (1989)). Various applications utilizing anode-acidified alumina nanoholes have been tried, and the nanoholes in question were reported to have an effect similar to that of a photonic crystal (Jpn. J. Appl. Phys., 38:L1403-L1405 (1999)).
An article titled “Green light emitting element with a coat made of electrically etched Tb3+electrically plated anode-acidified Al2O3” reports a light emitting element based on anode-acidified alumina nanoholes (Surface Technology (Japanese), 40(12):1405 (1989)).
However, conventional anode-acidified alumina nanoholes are formed only on the surface of an Al plate (membrane) which limits the application of the process. Moreover, for an Al membrane to be used as an electrode, it is necessary to remove a barrier layer from the bottom of each nanohole, and, if a process is introduced for removing the barrier layer, that process might disturb the uniformity of nanoholes in their size and shape.
As a solution to the above-described problems, JP, 2001-305360, A discloses a nano-structure having an embossed member attached thereto which is obtained by placing a membrane mainly constituted of Al on an electrode mainly constituted of tin oxide, and subjecting the membrane to anode acidification.
The anode-acidification described in said Japanese Laid-Open Patent Publication has a number of advantages. Since it is based on a wet method, the system therefore will require a low cost. Formation of nanoholes will complete in a short period of time. However, complete removal of solution used in the process left in each nanohole after the process would be difficult, and such solution left in each nanohole, if it were not removed thoroughly, would corrode or degenerate the assembly.